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<head><meta charset="utf-8"><title>Lifetime bounds in auto trait impls and generators #64552 · wg-async-foundations · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/index.html">wg-async-foundations</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html">Lifetime bounds in auto trait impls and generators #64552</a></h3>

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<a name="212479004"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479004" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479004">(Oct 06 2020 at 20:11)</a>:</h4>
<p><span class="user-mention" data-user-id="116773">@csmoe</span> so I just finished reading through your <a href="https://github.com/rust-lang/rust/compare/master...csmoe:issue-64552">changes</a></p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479034" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479034">(Oct 06 2020 at 20:11)</a>:</h4>
<p>I don't see any obvious problems</p>



<a name="212479077"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479077" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479077">(Oct 06 2020 at 20:12)</a>:</h4>
<p>however, what I'd do next is turn to debug logging to see the final param env that gets used</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479144" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479144">(Oct 06 2020 at 20:12)</a>:</h4>
<p>and to debug trait selection – see what candidates get considered and rejected</p>



<a name="212479253"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479253" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479253">(Oct 06 2020 at 20:13)</a>:</h4>
<p>from there you should be able to drill in to why the auto trait impl isn't being used</p>



<a name="212479282"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479282" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479282">(Oct 06 2020 at 20:13)</a>:</h4>
<p>(or maybe it is, and there's something going wrong downstream? who knows)</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/212479305" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#212479305">(Oct 06 2020 at 20:13)</a>:</h4>
<p><span class="user-mention" data-user-id="125294">@Aaron Hill</span> might also have some ideas</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/213970154" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#213970154">(Oct 20 2020 at 19:44)</a>:</h4>
<p>hmm, I'd like to review this branch I suspect</p>



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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187312-wg-async-foundations/topic/Lifetime%20bounds%20in%20auto%20trait%20impls%20and%20generators%20%2364552/near/213970276" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/187312-wg-async-foundations/topic/Lifetime.20bounds.20in.20auto.20trait.20impls.20and.20generators.20.2364552.html#213970276">(Oct 20 2020 at 19:45)</a>:</h4>
<p>I've been a bit nervous about how best to fix this</p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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